Around here
this solution got quite popular in the last 4-5 years for just that issue(Most people in DK drive comparatively small cars making subcompacts like VW polo, Ford fiesta etc. quite commonplace):
A special reason was that the local equivalent of harbor freight was giving away the tarp awning/carrier frame sets for free with the purchase of a trailer, with the logical catch being that the tarp would be Their company color (a radiant yellow) and have the Company logo on the side. RC'ers i've met with these just loves the yellow tarp, as it won't get as hot and dark inside as with the blue tarp, and most just covered the logo or lived with being a rolling commercial.
It sure get's you going in a hurry, just add a suitable carrier structure for your models of choice inside the awning and off you go!
But it wouldn't take much in the shape of wood or whatever to make a similar light removable frame and then cover it with on of those fairly cheap heavy duty tarps. Would get you going fast now and let you save the intricate trailer rebuild for fall and winter.
I guess the only drawback would be that you can't really lock your models up inside.
Seems not to be a big issue around here, but we do have a solution for that as well: A used tent trailer like this:
The size does put a limit to the size of ones models, but it'll be waterproof, strong, very light and pretty much ready to go. And usually quite cheap too, if you find one where the tent has rotted away. Won't really help you since you've already bought your trailer, but someone else might pick up on the idea.