Was hoping you didn't have a standard fridge, but knew some did.
If you don't mind paying the camp fee, you may want to check with KOA or other campground close to where you are staying. Not for storage, but for actual camp site. KOA is $31/night for a back in campsite. If you are willing to go by and check on the unit at least once a day, they may not be concerned with you having it there for a week without actually staying in it.
Ocean Lakes may also be willing to rent you a site for the week as long as they know you are coming by once a day to check it. Little more secure than KOA. Of course, Ocean Lakes is so busy and crowded, they probably wouldn't even know if you were staying in it or not.
Usually in mid March the campgrounds are not extremely busy and may like having the site rented for the week.
As others have said, next time look at Ocean Lakes, a place that has both Condos and campground. Then you could easily stay in the condo, keep the motorhome at the campground.
Bit expensive, but would recommend the Medevil Times dinner show. We've been several times, last few more for the food than the show.
Good luck and enjoy the family time in MB.
