I have one of tracks that hang on the spare tire. It should work fine on the trailer spare. You mike also sit down with a cool drink, see what scrap material you have on hand, use those ratchet straps, and come up with a something that would work. At least for a couple of trips. One of the trunk mounted racks could, most likely, also be adapted to work.
When you have some money this worked out great for me
I don't know if they make a hitch for what type of van you have
you didn't say what kind you have
but they do make custom ones also
I tow my trailer put the bikes on the front mounted trailer hitch bike rack
until then what your doing will work just not as easy
craigslist a cheap saris rack; I picked mine up for $40 and the straps worked fine for my suburban's rear doors.