We only accommodate motorhomes with trailers in select sites. It is seldom we can actually accept reservations with anything less than several months notice. The reason is a 40 foot motorhome with a 20 foot long trailer needs a site over 90 feet in length. There needs to be a couple of feet buffer at each end of the site, there is several feet of hitch between the trailer and the rig and then you need to have space to park whatever is being carried inside the trailer.
On top of that, such rigs need to have pull thrus with a very large turning radius, otherwise they have to drive across the adjacent sites to enter and exit. It just isn't worth the hassle and risk to put such rigs into anything other than the exact Goldilocks site. So once those sites are reserved (and we don't hold them specifically for motorhome/trailer combos, they are desirable for all big motorhomes, large fifth wheels and other assorted combos), we just say no.