There are a number of things working against you. First of all at 37' you have lost an awful lot of options at many state parks. Remember, most of these parks were created when a 30' trailer was really big & slideouts was not even a word. Next you have those who book a site way longer than they actually need. I can't count the number of times I have seen a class C or a B in a pick your own site park occupying one of the few long sites or pull throughs. It would be nice if maximum lengths were set for the long sites. Worst case of site abuse seen was in Alaska where a VW bus was occupying a site I later paced out at 75' deep.
Size does matter. The bigger you are the more skill you need to get into those sites that are marginal for your size & the more important it is to have a good director to get you in.