I would buy a fabric protector applicator gun with hose. Prochem UK sells them so USA should as well.
Get a 32/64 ounce cheap pumpsprayer.
Drill hole insert air pressure valve.
Add liquid,mini air compressor to fill.
No moving parts,cept for minor maintenance stuff over time .
You can change her easy.
Add another hole insert psi Gage.
Keep it in a wheeled milk crate.
Easy to bring in.
Mini compressor sits in box ready.
No batteries to buy,nothing to break,hot water comparable.
Toss it on a mini expandable hand truck also...
Options galore, inexpensive, long lasting.