Huffy,
PhotoMike has good suggestions. You want to work your way into a Expedition-style RV in a manner that won't trap you into something you really don't want in the long run. What is that? Only you can decide what your needs are for traveling. Write them down. Prioritize them. Maybe a Class C or small MoHo would be a better choice if you want to live a slightly more elegant lifestyle.
1. How small a space can you live with and live in? A TC is the most expensive per sq. foot of RV you can buy. Since you are sailors, you may be used to small spaces already. Be sure you have no claustrophobia if you go small. And, is this for long-term camping and traveling? There is a whole mindset and setup for full-timers and long-term expedition types.
2. Are you going to pursue an 'off-road' style TC? This changes the equation right away from a huge 4500 pound camper on an even bigger truck to an 1800 pound/wet or lower hardside or popup style TC still on a too-big truck. Always, always, always buy more truck than you think you will need.
Start by looking at used units, and getting buddie/buddie with someone who already has a unit similar to the one that you are interested in. Go to RV trade expos. The mfgrs. strut their new stuff at these and you can get a snootful of info that you may want to have. If you find a rig that you think suits your needs by all means take someone along with you that knows truck campers and RV's in general. This is crucial in making an educated choice.
3. If you decide on a certain rig, try out every aspect of it's design. Lay on the bed for at least 20 minutes to see if the mattress is meant for you.
Sit on the pot. Pick up the wand like you were going to shower. Do you do everything and fit in the tiny bathroom? I'm 6 ft./ 225 pounds and it's a squeak. If you are shorter than that, so much the better. Go thru the motions of cooking and pulling stuff from the fridge and cupboards. Are you going to use bottled water? Where does that go? Does this seem like a good set up? Have the two of you pass by each other in the aisle way. Does this ballet work for you? The most negative aspects of TC's for older folks (I'm older than you) are: 1. Climbing the outer stair steps easily. and 2. Climbing the very tall two steps to the overhead bed. There are legions of people with bad knees and backs who are forced to sell their TC's and buy an almost no entry step-up, class C.
The largest and widest spectrum Truck Camper community is over on the RV.net/truck camper forum. I would skip on over there and sniff around for lots of info on getting your feet wet in truck camping. Post your querrie and you will get a lot of hits from people who know.
Jeanie and I are retired and are planning a 16-week clock-wise circumnavigation of the U.S. boundary states; states that touch an ocean, or Canada or Mexico. We've been almost everywhere west of the Front Range and this will be a new opportunity to see the eastern half from Sept. 1st to New Years day. Our twist is we will try to camp on the beach at every beach that allows it, right on the sand. Because we can. There are surprisingly a lot of beach camping (not much in Fl) available and we'll be there off-season.
regards, as always, jefe