How long is too long for camper

I am leaning toward the 84". Like I said the total length and wheelbase is about the same a regular crew cab with 8 foot bed, but instead with a 10.5' or so flat bed.

I am looking at a company called camperlogic.com for the camper, they have a build thread on this expeditionportal website, and it seems like its' pretty well built and insulated.