As mentioned thousands of RVs are stored there for the same reason as you mentioned.
We visit MB yearly but storing at MB wouldn't work for us since we also visit relatives elsewhere.. We see a lot of RVs brought in from storage every time we are there, must be a lot of satisfied folks.
If it was our sole destination it would be a consideration.
Downsides are it is stuck in one place so if you want to camp elsewhere it would be a very long drive to get it to do other camping.
Cost, I suspect MB storage costs would be higher than non beach storage (tourists destination costs are higher). Depending on campground you might be stuck staying at that campground because of the storage lot is theirs. Not sure if there is independent lots and movers which would allow you to choose what campground you want to use, you would have to check into that. Setup costs can vary depending on level of service you want from basic move to full leveling and hookups (even turning on fridge and A/C).
If the costs and/or limitations are acceptable to you then perhaps give it a try.
As said, you most likely will need to make sure no food/drinks/trash is left behind in the RV. Bedding and stuff might be fine but you might wish to pack in some mouse proof containers for storage.. Would be a buzz kill to get there and find your stuff has been gone through by mice.
