Pat,
You know this is somewhat like that eternal chain of buying a house, adding a porch, roofing the porch, windowing in the porch, then needing an open porch, etc....
For me, overnighting on the road on the way to a new marina works well in the TomCat, but it is not fun to have to climb up and down a million times in a long term campsite. I have seen how well Bill and El get along "boaterhoming" in person, but they seem to be pretty unique ppl!
I have had trailers, but prefer the motorhome of some kind for "exploring", where you can just stop on a whim to explore and come back to a heated or A/C'ed environment, change clothes, eat, take a quick nap in a Wal-Mart lot, etc.. Also, you can eat going down the road, nap comfortably while another drives, etc..
5 years ago I bought Holiday Rambler's entry level diesel pusher, a Neptune 32 with aluminum body and a smaller Cummins 275. The aluminum model is about 3800 lbs lighter than the comparable fiberglass ones, so it can get up to 14 mpg (going downhill, with the wind, without running the genset). Going 75, running all three A/C units and the genset, TV, etc., we usually get 9.3-9.6 mpg over our last several 3,000+ mile trips. The 275 can only pull 3500 pounds, but the newer models all have 300 or greater HP Cummins engines with a base tow limit of about 5,000 pounds.
These Neptune units are made by Monaco Coach and most of the components are the same as these luxury models. The Cummins engine service interval is once every 100,000 miles other than oil changes at 15,000 mi intervals. The shorter 32 foot model with slides allows a lot of room, use with slides in or out, and the 45 degree steering let us parallel park in most places where 2 normal cars fit.
So, an entry level model of a diesel pusher manufactured by a large, high quality company will get you most of the bells and whistles and reliability at a much lower cost, especially considering today's economic realities. Most of us could not sell our motorhomes for what we owe on them.
If you're looking at motorhomes, I'd advise a short unit, diesel pusher with slide outs that permit using the unit with them in. We have not yet needed a towed car (dinghy or toad). If we really need something like that, we can easily rent a car locally. The money you save on towing gas could easily pay for a rental. The shorter, sharp turning motorhomes can be used for many errands and shopping, giving you the luxury of A/C , privat bathroom, rest stop, and clothes changes any time. Some friends of mine mount scooters on the hitch for most running around.
Another thought, looking at what is happening at the large marina communities from the Gulf Coast, Texas, Missouri, Arkansas, Oklahoma, and Kansas is that they are NOT very busy and many have cabins or condos for rent by the day, week, month or year for a song right now. You could overnight on your "boaterhome" (I hate to leave mine alone in a motel parking lot anyway) in Wal-Mart or a truck stop and then luxuriate with a covered slip and a walking distance cabin/condo.
Good luck!
John