We are planning on a 2 weeks campervan road trip around Iceland in May 2019.

Right now the draft plan is as follows :
Day-1 : Arrive in Reykjavik by 1300 hours and stay
Day-2 to Day-12 : Campervan road trip, mostly anti-clockwise
Day-13&14 - Stay at Reykjavik and depart

Route : Keeping it flexible. We understand that few campsites will be closed in early May. Also the highland roads will mostly be closed. So, dropped the plan for renting a 4 X 4 campervan. This is our first trip and we will stick to the primary attractions along the ring road.

Campervan - This is the most important factor for this trip as it's comfort and reliability will have a big influence on our tour experience. We checked out few options - Kuku Campers, Camp Easy, Cozy Campers etc. Kuku is cheapest but I read few reviews with bad experiences - older vans etc. Cozy campers seems to be a good choice based on internet reviews till now. This is one area where I am looking for inputs.

Activities - We are reading up about a few activities that we would like to do - whale watching tour, glacier walk and may be diving between the tectonic plates. Need recommendations for these too on good tour operators.

Any other suggestions on the overall plan - please feel free to suggest.

Thanks.

It will be cold in May for sleeping in a car/van. Wouldn't it be cheaper to rent a car and stay in small B and Bs with heat and indoor plumbing (I am not a camper, but I was in Iceland May 2017 and it was quite chilly at times and warm at other times. Not sure I would want to be sleeping in a car/van. Gas is also very expensive. )
There are many great tours and they are expensive as well. Nothing is cheap in Iceland, not even food. On the plus side, It is a very friendly country and you really never need cash for anything, your credit cards work everywhere. The landscape is quite unusual and beautiful.
Whale watching is something you can book day of at the docks in Rekjavik. I would watch the weather. You want calm weather for the boat ride. They hand out sea sick pills and barf bags as the boat pulls out. We went on a very calm day and once out in the water, it does get rocky, but we had no problems and we did see whales.

https://adventures.is/iceland/day-to...-snowmobiling/
We used Arctic Adventures for a Super Jeep and snowmobiling tour. It was a lot of fun!

Thanks. May will be a bit cold but we are planning to rent campers with good heating systems to hopefully manage that. The main motivation for campers is the flexibility of brings in.

For whale watching, we are thinking of taking this from Husavik. Any recommendations ?

You may want to check if campgrounds are open in May as wild camping is illegal in Iceland.

Thanks. Yes, I am already checking which camp grounds are open and making a draft route accordingly. We will anyways have a backup option of getting a hotel room in a nearby town incase the weather gets to cold or the campground we arrive at is closed.

Actually we are yet to finalize on our camper van rental company ? And also if the 3 bedded camper will be spacious enough for 3 members for 2 weeks.? The next option is 5 bedded bigger vans but that comes at a cost - difficult to drive, more risky in high winds, higher fuel costs and higher rental costs. Looking for some inputs here..

How old is the third person? WHich model of camper are you considering? Most three bed campers are aimed at two adults and a child.
Of course it is feasible to spend three weeks in a camper, especially if the weather is half way decent, but you have to allow each other space and really like each other.
We spend 5-6 weeks at a time in a two berth camper. No TV to entertain us, and quite often no internet either. It gets fraught at times but 99% of the time we love it.

Have a look at Campercontact.com for campsites and camperstops.

Our group will be myself, wifey and our 11 year old son.
We are looking at hiring the below camper or something similar

https://cozycampers.is/fleet/cozy4/

We will have another similar sized family accompanying us in another similar camper. We are close friends, so hope to spend our time well at the end of the day cooking food and spending time over dinner.

Will check out the link you shared. Thanks.

I think the cozy 4 is too small. You need the cozy 6. Remember your 11 year old will want to go to bed before you do and there is nowhere for you to sit once he is in bed. The Crafter is still not a huge camper, and it will still be tight with the three of you, but certainly more comfortable than the Trafic.
Try to find a camper van which offers a seperate bed for your son, and prefereably has the front seat turning round so you have a place to sit once he goes to bed.
It may be warm enough to sit out ( or dry enough with warm clothing) but you have to reckon on cold and or wet as well.
I haven't looked at the price of it but even something like this would give you more room and your son his own bed. https://www.campericeland.is/en/flee...amper-premium/

Sorry if this is too late but we did something very similar in September. Our van didn't have a separate heating unit and we were fine overnight with the blankets and sleeping bags provided by our rental company (Snail). Some people might have been cold but we were okay with some long underwear and the bedding provided. I think May is similar in terms of weather to September. It is good advice to confirm that campgrounds are open though. It will absolutely, 100% be cheaper to rent a van than to find other accomodation. Additionally, it provides you with so much flexibility and independence to be able to travel as far as you want each day and not have to be a slave to your pre-booked hotel. This was the first time I had travelled by campervan and i loved it. Make sure you park in a designated campground each night and consider having your showers at local pools/hot springs. Enjoy.