I contacted PT shortly after I purchased my tt asking about the same thing. As RV Guy stated, they use Dicor on the roof. On the sides of your tt they use TremPro 644 RTV Silicone made by Tremco.
Here's some addtional info that I received from PT.
I contacted Prime Time this morning with some questions about how the caulking should be applied to the outside running lights, etc... I received the answer this afternoon. Here is their reply;
The marker lights (clearance lights) are to having caulking on the top and on the sides, only the marker lights on the front cap will have the caulk all the way around them. The external speakers will not have caulking, only the putty tape underneath them.
Hopefully this info will help you.
Gary & Trish
"PT Crew Member Since 11/2010"
2017 Prime Time Crusader 315RST TE 6.0 : 2007 Flagstaff 206ST MAC Series
2012 F-250 Lariat : FX4 : CC : SB : 6.7L Diesel : 3/55 Gears
2016 Nights Camped - 9