The router is in the RV.
DD-WRT is open source and free. It replaces the software on your router (firmware). The interface gives you many more options. For example, my Asus WL520GU had a bridge mode capability but the client computer had to be connected by cable. DD-WRT allows me to use the router as a wireless
The various price points on routers usually determine the amount of features available even if the hardware is capable of much more. DD-WRT lets you access the features usually only available on more expensive routers.
I tried it on a DLink DIR-615 rev E but could not get it to work as a wireless bridge. It had an Atheros chipset. Routers with Broadcom chipsets will work.
My Asus WL-520GU is a B/G router. I just got an Asus RT-N12 B/G/N (Broadcom chipset) router (approx $40) that I will load DD-WRT onto to see what the greater range of the N specification will bring in. Both Asus routers have detachable antennas. That means I can connect exterior or directional antennas. The DLink DIR-615 rev E antennas were not removable.
The town (just across the river) has free wifi. It'll be fun to see if I can connect to it.