Bring a couple of tarts with you, one for under your tent, and one to put over your tent.
Hmm.... Interesting use of "Tarts"
Just kidding (I know you meant Tarps), I just couldn't resist.
We like to camp in the rain, but we usually have a warm fire going and I know you cannot do that at FW.
Not true, you can have a fire, just not an open pit fire. You have to use an enclosed fire pit that will keep sparks and embers contained. There is a list of approved campfire pits
http://allears.net/acc/fw/campfire-pits.jpg However, it's certainly not the same as an open pit fire.
In all seriousness though, I hope you go despite the weather. Particularly if this is your "Test" camp with the tent. Testing things in perfect conditions is NOT a way to test it. You want to test in adverse conditions to truly evaluate it.
My pieces of advice in addition to what has already been mentioned, is if it's raining, RESIST touching the inside of the tent. Depending on the material (Probably nylon?) when you touch a "Wet" Tent, that's a spot where moisture will like to come through.
Also if you have time and the ability, I strongly recommend using a water repellent on your tent such as Kiwi Camp Dry (or similar). Pay particular attention to the SEAMS. Coat the entire outside of the tent. Also worthwhile to spray the seams on the inside too if you can. The problem here is that you need to let it dry completely. Typically you would set the tent up, spray it down, let it dry (over night) and then re-pack your tent. Depending on timing you may not be able to do that. Alternatively, if it's NOT raining when you get there, you can set up your tent, and spray it down with the camp dry there. You just want to make sure you have several hours to let it cure/dry. Ideally a full day but even if you get 8 -12 hours, you are better off then without it.
Either way, I hope you have an awesome time.