For the Fairplay area you need to do Wheeler Lake. Great views and a couple of obstacles to play around on. I've parked a 28 foot gooseneck right before the start of the trailhead with no problems.
For the Buena Vista area there are a lot of trails: Carnage, Chinamans Gulch, Mt. Antero/Baldwin Lakes, Grizzley Lake, Iron Chest, Tincup Pass, etc....
There is a place in Johnston Village (just outside BV) that you can park a trailer. This is usually where I park the gooseneck when doing any trails in the greater Buena Vista area. You can fit a trailer at the trailhead of Chinamans Gulch/Carnage and depending on what other trails you are going to do sometimes you can find a spot along whatever dirt road leads to them. I suggest you ask these same questions on Colorado4x4.org as this site is more specific to the area that you will be wheeling. Also check out traildamage.com.
Feel free to PM me for more info as my posts are delayed due to my post count not at 25 yet.