^ good advice there. This is kind of what we did:
(oops, TT = travel trailer, TV = tow vehicle)
-Identify the layout you WANT and can put up with for years. That takes the longest time...at least for my wife.
-Identify manufacturers with that floorplan. See if you need additional insulation packages based on possible destinations and times of years you may travel. Allow for outside the box thinking :) Research manufacturers backgrounds/years quality issues, once you settle on several candidates. Can you fix them easily if they have issues.
-Match the tow vehicle with the trailer. Assume the worst possible weight scenario - i.e. taking everything but the kitchen sink. Then see what you can live without. Then prioritize what you REALLY need vs. want. If you're not enjoying the trip or the camper, you're not going to have much fun. Also, is mpg a factor, is year of TV a factor, can you fix tow vehicle if you break down.
-Consider anti-sway bars/weight distribution hitches. Let me tell you, towing even a popup camper through high crosswinds (did it in South Dakota once - ONCE!) can result in white knuckles pretty quickly.
-Allow time for things to go wrong...and to go right. If you find you love a specific location, I don't see anything wrong with going there more than once, or changing travel plans.
-almost forgot this one: have a spare tire for your TV AND your TT, or at the least a backup plan like AAA/Good Sam towing or what have you. You'll likely identify other things that you really should bring a spare of during your camping activities. Maybe extra propane, batteries, etc
-Once you find your "perfect" combo and you've done the math with gross weights and you are POSITIVE it will tow, ask dealer to borrow it. Go weigh the combo on the scales, so your tongue weight/gross weight is known and can be adjusted. If possible put enough stuff/weight in the TT so you are basically ready to go camping before you weigh.
Bah. I started typing and found myself getting buried in work. I'll let others chime in with more help.