Electric extension cord - what kind?

It all depends on what you plan to run. If your not running big heaters, AC or any huge loads, a 14 awg cord is fine.

#12 wire minimum, #10 is better and required if supply is 30 amps.

That #16 cord would be better known as a fuse.

Harbor Freight has nice 10 gauge cords in 25, 50, and 100 foot lengths. Highly recommend. You can even cut them up and make useful things out of them.

+ 1 on at least 10/3.

You are going to want something like this.
10/3 cord

Maybe you can tell us what kind of a camper you have, whether it has an air conditioner, etc.

Most campers are going to have a 50 Amp or 30 Amp connection. If your has a 'normal' wall outlet (like you have inside your house) you still need a cord rated for 20 Amps like this one...

Utilitech 100-ft 20-Amp 110-Volt 10/3 Yellow Outdoor Extension Cord

Do you want to run the ac and microwave or just lights and fridge?