Just installed the Power Watchdog EPO 30A internal, and it works great. For me easy install, power into trailer right inside removeable panel, and if we ever were to change trailers, easy to remove. Bluetooth is great, works well with good info about usage. I always check with homemade devices just like others have posted. Even if I didn't, the Watchdog would act if there were problems!!! Installation ease should be a determining factor in your choice.
MDKMDK: "you're most likely going to have to exit the vehicle at some point to resolve the problem" How did you plug in in the first place!!!!!!!