Adding New cars to GmodRP?

Hello Facepunch, longtime gmod player, and decent timed lua coder.
I signed up to try to get my question answered, but before posting i searched the forum for a possible match, which there was none.
My Friends and I have been recently running a private server with gmod RP on it, yes i know a little old but its still good RP, unlike DERP. but recent we have been trying to add new cars to it. other than jeeps and airboats… I have had little luck adding more than one car. which is based off the perp willard model.
if the code is necessary I am willing to post it, its not perp though its GMOD RP code with a perp model. I am asking for this help, for the fact that i can not find any info on the web.

thanks for all help,

bump thread please