Is your Subaru front wheel drive? (I had thought that all Subaru's are all-wheel-drive)
If it is AWD I doubt you'll be able to pull it on a dolly.
Having said that: We use the EZ-Tow.
At the campground:
I will usually unload it in front waiting to check in--unless we get a pull through site. If I have a pull through site I'll just wait and unload it at the site. It really depends on the campground we're staying at and where is it the easiest to unload/load.
Once unloaded I pull up to the campsite ready to back in. Unhitch the dolly and walk it back to where I want the rear of the camper to be. Then I back in on top of the dolly.
Yes you can store it under the rear:
Here is our C-Max on the dolly:
Not sure how a kayak would be affected by that. You do have some options, though: Since the 25.4 has a ladder you could hang the kayak off that or even strap it to the roof of the camper.