How about an outlet for the RV so the owner can plug in a battery charger, water tank heater, etc?  

Point-and-shoot camera (I take a couple hundred photos per property, which uses a lot of space on my phone and drains my battery quickly). 

Then some PM charge a service fee every time they send someone to service the property or if they go to inspect the property - in other words, you might get nickel-dime'd with all kinds of other fees, that could easily raise the "PM fee" to 12%+ (we once got charged $45 service fee + $9 per battery to change the smoke detectors batteries at make-ready).Regardless, you need to factor in at least 8% PM cost, even if you self manage (after all your time costs too) as there might be a time when you might want to (or be forced to, like sickness or old age, or desire complete passive participation) to be completely hands-off and you'll need a PM.

Downside of these - batteries die, and not always reliable in very inclement weather.

Due to the fact that batteries go bad and wireless systems can get frequency interruptions, hard wired systems are the most reliable and desired by fire marshals and Inspectors.

Hello, By law does landlord need to change smoke detectors batteries or it's the tenant job.

For your situation, maybe you could look into consumer grade battery operated cameras?

They were a blessing that saved the project and they continue to be what I think about to cheer myself up when I'm blue.My remodel investment was as follows:Property: purchase price + interest, taxes, escrow, whatever = $25,910Other Carrying costs: water = $241Demo & Hauling: $580 (Craigslist Find)Water Main and Hookup: $1,890Septic and Leech field: $4,250Concrete, Framing & Roof: $17,406DIY Exterior Paint: $470Plumbing: $5,953DIY Solar System & Batteries: $14,181Electric Wiring & Lighting: $880 (Husband is an electrician)Mini-split Heat Pump $2,000Insulation, Drywall, Primer: Plus "shiplap" style wall to cover fed up drywall - $4,489Floors: $3,327Interior Paint & Trim: $520Tile: $5,129Kitchen cabinets, shelves, countertop, sink, etc: $2,483Appliances: (range, hood, fridge, dishwasher, washer & dryer) $1,679Bathroom: (bath, shower, vanity, trim, etc) $1,448Fence and Patio Cover: $3,900"Landscaping": (gravel, shower, tiles, lights, etc) $1,048Furnishing: $1,518Housewares & Decorating: (many from my house as we were moving) $150It took over a year to finish since I ignored it the first 6 months and could only do the occasional weekends once I got started. 

They were a blessing that saved the project and they continue to be what I think about to cheer myself up when I'm blue.My remodel investment was as follows:Property: purchase price + interest, taxes, escrow, whatever = $25,910Other Carrying costs: water = $241Demo & Hauling: $580 (Craigslist Find)Water Main and Hookup: $1,890Septic and Leech field: $4,250Concrete, Framing & Roof: $17,406DIY Exterior Paint: $470Plumbing: $5,953DIY Solar System & Batteries: $14,181Electric Wiring & Lighting: $880 (Husband is an electrician)Mini-split Heat Pump $2,000Insulation, Drywall, Primer: Plus "shiplap" style wall to cover fed up drywall - $4,489Floors: $3,327Interior Paint & Trim: $520Tile: $5,129Kitchen cabinets, shelves, countertop, sink, etc: $2,483Appliances: (range, hood, fridge, dishwasher, washer & dryer) $1,679Bathroom: (bath, shower, vanity, trim, etc) $1,448Fence and Patio Cover: $3,900"Landscaping": (gravel, shower, tiles, lights, etc) $1,048Furnishing: $1,518Housewares & Decorating: (many from my house as we were moving) $150It took over a year to finish since I ignored it the first 6 months and could only do the occasional weekends once I got started. 

They are usually responsible for anything consumable like light bulbs, smoke detector batteries, filters, etc.