Replace the tent first. A leaky tent will turn your nice sleeping bag into a cold sponge. My second backpacking trip ever was a miserable experience due to a leaky tent.

We were in the Bob Marshall wilderness and it rained for 3 days straight. A very cold rain. My $30 tent leaked from the top, bottom, and sides and my wife and I had one very saturated sleeping bag and one partially saturated sleeping bag. We attempted to cram into the one semi wet bag (we're skinny) and we shivered and froze every night. We also had to cram 3 people into one 2 man tent. It was a "fine and pleasant misery".

Get a good quality tent, tarp, or tarptent and make sure you seal the seams if they are not sealed by the manufacturer.

-Skippy