I've used my 500 on short credit-card tours without any problems.

I wouldn't use it on unsupported camping tours without a reliable source of power -- which would have to be shared with all your other electronic goodies.

You can load courses into the 500, it just doesn't have street names. As long as you can follow simple instructions (left, right, straight) you won't get lost. If you go off course, the device lets you know what direction to get back on course, as well as your off-course route. If you ever do get seriously lost, you can either refer to a map, a smartphone, or a friendly passerby.

To be on the safe side you might want to keep your pre-loaded courses below 50 miles each, as the 500 tends to crash with very long courses.

With the 800, keep in mind the maps need to be updated as they would on a regular GPS. I believe nowadays Garmin is doing "lifetime updates" on their new units, so you'd get the Continental US included. That means you'd have to buy any international maps you happen to need.