I've used NOCO chargers on my AGM house battery with good success. The terminal connector and extension cord accessories are what make this so handy.
Zip tie everything down and secure the plug end to a convenient access point. Plug and play.
This adapter might be long enough to get you outside access:
If more reach is needed this will do the trick:
Despite what the amazon picture shows, there is an attached weatherproof rubber plug cover that is present to waterproof the plug-end when not in use.
2003 E-350, 5.4 V8, 2x4, LSD 4.10, WeldTec 6" lift, SMB, Penthouse
2016 Beta 500 RS
2014 KTM 350 EXC-F