I don't think it's the cheapest, but I've bought 2 of California Car's Satin Fleece Stretch Fit Indoor Custom Car Cover with Fleece Lining, custom cut for the 05/6 GT, extremely soft inside, dust cover only / would not be waterproof, fits perfectly with no wrinkles and goes all the way right down to the floor to keep dust off the wheels and underside of the car. I paid $303 total w/ ship Sept 2020; prob higher now, but they may have coupon codes out there. It's so nice I bought a 2nd one for our 2nd GT.
There seems to be a lot of car cover makers out there, and I know from reading on this forum that guys here have owned others, possibly as nice as these CA Covers, and maybe cheaper.
I've never owned or experienced a car capsule, but FYI a shipper showed up today to transport my recently sold GT to its new owner, and he covered it with a very lightweight clear plastic wrap that had an elastic band around it. It was big a baggy but completely covered the entire car, and might be sufficient depending on what you're wanting / needing. I don't know the name of it but just texted the driver to ask. I'll post again if he replies w/ anything.