A router will not address a weak WiFi or a weak Cellular signal so if that's what you hope to improve you will need some device the adds an external antenna to the roof, pole or ladder.
For campground WiFi you can do an inexpensive set for less than $100 but it won't help cellular. There are also cellular antenna/amp setups (Wilson Cradle is very popular) that will help with that side. They are very different signals and require different types of antenna for reception. If this helps, let us know what you would like to do to help with your signal reception.
