Designing Kitchens and Bathrooms - tub surround

We recently purchased a new wall surround. I just got so fed up with doing the caulking bit every 6 months or so because it wal always springing a leak somewhere, and we also purchased a tub (i guess its fiberglass) to go with the wall surround, because Lowes told us we were doing things backwards by putting the wall surround up first. They said the tub could go right over the existing tub. I have already been told we can't put the new tub over the existing one in another thread. My question is can we keep the ceramic tub we have now and just put up the new wall surround, then in a few years I can start with the crappy caulking again. I thought I could stop (the caulking) by buying the tub to go with the wall surround. We are not rich people so what would be the best way to get this wall surround up with the old tub and not have it spring any leaks years down the road, because I have had it with the leaking every few months. Sorry this is so long

The reason the surround goes up last is so any water will run into the tub. You can put up your new surround with the old tub. Try to keep the bottom edge of the surround within an 1/8" of the tub. Make a mark on the existing surround and take a measurement. Step into the tub and measure again to see if the tub flexed. If it has, before caulking, fill the tub as full as you can with water and maybe even some concrete blocks (on a towel to protect the tub surface). Make sure all surfaces are clean and dry and caulk. Let it cure fully before draining the water. This will help prevent the caulk from pulling loose. Good luck.