Seems the esteemed Mr. B and I agree often.  I use a T135.  Couple of
reasons for the selection.  This unit works, is CoastGuard certified and
accepted as a "toilet" device by those various National Parks and Reserves
that REQUIRE you to carry such if you overnight in those areas.  Canyonlands
along the river is such a place. Kane Creek Cyn.

The addition of a T135 legally makes you a self contained RV and opens a few
doors under that designation.

Easy to use, no detectable odor, easy to clean, will fit between the seats,
under the extended bed but not in the ashtray.

See em at http://www.thetford.com/portable_100.cfm

Available at sears, campingworld, and other fine purveyors of scatological
accessories

pensioner