How difficult is it to get from LHR to the Waterloo train station (2 adults with 2 bags)?
Approximate cost and time would be helpful in addition to mode of transport. Thanks.

Use this: http://journeyplanner.tfl.gov.uk/use...T2?language=en

That seems to favour the Heathrow Express as an alternative to doing it all by the tube. Another option is to get the bus to Feltham and suburban train to Waterloo from there.

If the aim is to take a train from Waterloo to somewhere else in the south-west, it might be worth looking at the links that avoid going into central London:
http://www.heathrowairport.com/trans...rail_air-buses

Forgot to amplify: of the options favoured by the TfL journey planner:

Heathrow Express to Paddington, then tube to Waterloo: expensive, not much less for two than getting a car service, and not much time saving over the regular route by tube.

By tube: Piccadilly Line to Hammersmith, cross the platform for the District Line eastbound to Westminster. If you're aiming to get to the hotels at County Hall, just walk over Westminster Bridge from here, otherwise change (escalators down) to the Jubilee Line eastbound to Waterloo.

We need to get to Southhampton from LHR. I was looking at Megatrain but it seems it will probably not be a savings since it isn't cheap/easy to get to Waterloo.

Easiest may be National Express coach, although you'll have to go into London and out again. You won't have to go anywhere IN London, though, just off one coach and onto another, and it will go to the cruise terminal, if that's what you need.

There is no need to go into London and out again, as there are direct coaches from Heathrow to Southampton. Just check the National Express website.

I did check the National Express website, and it didn't show any direct coaches. I may have been checking a weekend rather than a weekday, though.

"I did check the National Express website, and it didn't show any direct coaches."

There are direct nonstop coaches every couple of hours seven days a week.

More frequently, there's a railair bus to Woking, connecting with about three trains an hour to Southampton.

It's highly unlikely that there's no financial saving getting the Megatrain. Spend two seconds checking the numbers and the poster will see that the absurdly low Megatrain prices more than wipe out the trivial tube cost. Megatrain's not meant to be the most convenient way of travelling: but it's incontestably the cheapest.

On the National Express site, you might have to adjust the detail of your start and finish points - you'd probably need to take local transport from Southampton Coach Station to the cruise terminal, for example, or between the Heathrow terminals.