Very good to start looking at hdt's. Have you looked around at the Escapee's site?: HDT - Escapees Discussion Forum
They also have a marketplace section on their forum and there are hdt's for sale there now: RVs, Tows, and Toads for Sale - Escapees Discussion Forum
Keep us posted and for sure feel free to pose any particular questions here because there are some experienced truckers on here. Good luck with the search.
'03 Freightliner FL112, 295" wheel base, with '03 United Specialties 26' living quarters, single screw, Cat C12 430 h/p 1650 torque, Eaton 10speed , 3.42 rear axle ratio