Cement blocks aren't a bad idea, but more than likely you're going to have some settling over time. Would it be better if you make a base with 4" cap blocks then use threaded stabilizer jacks to put tension on the frame? This would allow you to easily adjust as things shift and move.
My old TT was 34' and always felt bouncy. I started putting a set of these jacks just in front of the axles and firmed things up quite a bit.
KJ
'14 Ram 2500|Crew Cab Long Bed|4X4|Cummins
Curt Q20 with Ram 5th Wheel Prep
2000 Crownline 205BR
1997 Ranger Comanche 461VS
'01 Polaris Virage TX PWC
'94 Polaris SLT750 PWC
3 Wonderful Sons (21, 15, & 13)
1 forgiving wife!!!