I would like to tie into the brake light's of the R/T for when its on the trailer, so when the trailer lights come on so do the brake lights on the R/T. I would use some sort of weather pack for easy hookup..

Will I have any issue with backfeed or anything else?

The trailer is grounded through the ball and I have a 10g wire direct from the neg terminal on battery strait to the plug for the trailer. The lights are 16ga iirc.