Garages here can get very hot in the summer. I would only store items impervious to heat and humidity there and nothing at all in the attic. Use only metal enclosures in the garage, nothing made of particle board that invariably warps, molds and attracts bugs. Clothing, electronics, photographs and art supplies should be kept in an air conditioned space, perhaps locked in a coat closet, pantry cabinet or walled off half of a bedroom closet. Toss in a couple of borax type roach traps. Regardless of what you store here while away, take all true valuables and vital documents with you.

rent an airconditioned 5 x 10 storage space at FT Knox self storage or a different self storage. just make sure it is climate controlled(air conditioned)

We have rented out our house for 4-5 years. We have a ‘coat’ closet in our house; we got a ‘key’ lock for it and store some of our pantry food and cleaning supplies and paper products. My husband put 3-4 shelves which worked very good. we store heavy things in plastic containers on floor.
Another couple, bought a storage thingy and put a padlock on it and stored it in their garage with no problem.
We also got a new NEST thermostat installed and I can use my IPhone anywhere to turn up/down temperature. The nest is a little tricky but I’ve gotten use to it. (On our contract, with renters, we pay $150 for electric; if they go over that amount, they pay. We usually deduct it from security deposit.)

We stored our personal items in the guest hall closet. Changed out the door handle to one with a key. Used plastic totes and space saving storage bags for extra space, simple solution. We also used a few cabinets in laundry room and used a slide lock. Never an issue. It helps if you are a packing genie 😁.

Using a dessicant like Damp Rid will help keep moisture down in a small space. We also have the plug-in ultrasonic bug repellents. Just two more ideas.

We use one of the bedrooms, we have a 3 bedroom, to store our personal things. Put a heavy duty deadbolt lock on it and have never had a problem renting or with someone trying to get into our locked room. We're on a golf course, rent it out the winter months as a 2 bedroom. Consider using an interior bedroom or a closet with a good lock.

I wonder why anyone would rent here for the summer, but if they do I wouldn't use the garage for storage, I would use a closet in the house or a climate controlled storage unit.

Den or 3rd bedroom storage
 

I know people who put all personal belonings in a locked den or 3rd bedroom.

You might want to look into renting storage many are temperature controlled. As to critters, it is simply amazing what they can and do get into. Ex New yorker-us too.
A mouse can squeeze through a less than 1/4 inch crack. Here perhaps less that that.
Lizards, they seem to go through walls with no cracks required.

Anything is possible! Storage of your items out of your sight OP, tenant or otherwise is a risk. Trust me!

We had this same issue...luckily the master has 2 large closets, we took one and put a key lock in the handle, so renters only get one very large closet per room.

Summer rental
 

We plan on renting this summer (July, August & maybe September). We will be house hunting with plans to be living in TV before winter.

We just did this: If you have a coat closet in the front hall, replace the door handle with a locking handle that matches the rest of the house. On the upper shelf store your wine, spirits, etc... Clothes that need to hang can go where the coats would go. Store the clothes that don't need to be hung in bins that are not too wide and stackable. Golf clubs can also fit in that closet. For yard stuff and tools, buy a locking metal cabinet for the garage like a Gladiator.

I would only rent to friends. They can use anything I have.