Quick question, does anyone know back in the day if they sprayed color under the truck bed.
Mine is a 46 international K-1. I know the cab is red underneath but the bed was too rusted to tell. Plus didn't know, if that's a no brainer,to save on extra paint cost. Just finish the whole thing in DP90. Was thinking just leaving the black epoxy there and save some paint. Kinda would not like to use under coating in case i change mind or just want it clean under there.
Thanks.

kinda sounds like its up to you as you've said the extra cost of paint color and the extra work is a negative. if it were me, I would epoxy it then spray it with under coat. same with the fenders the undercoat will help deaden sound and protect the paint from rocks flinging off the tires.
but its really up to you and what you want.
Jay D.

Skip the DPLF 90 for the belly and buy PPG CRE epoxy or PPG HSP black. Even ********** is cheaper than PPG DPLF. DP90 was great and discontinued long ago. I own a restoration shop, and never use undercoating unless duplicating a factory procedure for a car being judged for points, or the owner requests it. Even then is has to be shot correctly to be assembly-line correct. None of the cars I've restored in three decades have failed because they lack undercoating.
Doubtful your truck had painted floorpans. Most likely some body overspray over the primer. International forums would have data and reference.

Undercoating is a generic term tossed around by novices. There are other products available that perform better than poor quality undercoating.