Be aware that once you get the right connection for the grille to van propane you might have a problem with getting the grille to operate properly.
Most grilles are made to work of the little propane bottles, which are full pressure bottles, not the low pressure like used for the inside cooktop and furnace in the van and Roadtrek calls the propane pigtail you will be hooked up to "high pressure". I reality, that pigtail is regulated down in pressure. Roadtrek literature says it runs at 15 psi, but it appears that the regulators are really at 10 psi so about 1/10th of what the little bottle pressure would be.
Many grilles work just fine of the the 10 psi if they are rated for the bottles, although with slightly reduced heat output. Some, however, will barely get warm at all on the 10psi. The Coleman grilles and stoves I have seen seem to be mostly in the bad category. Our Magma grille was fine.
I think it mainly has to do with some grilles and stoves like the Coleman have a what is probably a backflash arrestor in them, which is just a small porous brass filter looking thing in the regulator input. They are pretty restrictive and can make it so way to little gas gets through to the regulator at only 10 psi. I have heard of people removing them or drilling a small hole in through them, but can't really recommend that as you might then get too much flow depending on what regulator they used.