Battery maintainer
 

My panel is gonna sit in storage for about 3 months. I just hooked up a maintainer inside the vehicle. Anything wrong with putting clamps on the postive and negative battery terminals. Manual for the maintainer says the ground should clamp to the chassis. Anything else around the battery I should clamp on to?

Attaching to the neg battery post is just fine. Attaching to the chassis is likely advised to keep any resulting sparks away from the battery while attaching the clamp.

You could put it under the hood.

I would follow the manufacturers directions, unless the battery is disconnected at the negative terminal