For your purposes, look for a BlueTooth GPS that has a long battery life (so you can keep it going in the wilderness) or one with replaceable batteries so you can carry spares and swap them out. If you don't have BT, then a good CF GPS will do you well. There are some really reasonably priced ones out there. Given that you will be under trees, which attenuate the satellite signal, look for something with either SirfStarIII or MTK chipset. The both work better in degraded signal areas than the older chipsets.
For maps, MemoryMap is a pretty good solution, as are some others. There is a website at
GpsPasSion - Reference site GPS that has some good forum discussions on terrain mapping.
There are reviews of GPS products
here.