The roof has been fixed, so raining indoors is not really a worry anymore. However we do have lots of bats. We love the bats. They eat the flies and other bugs that used to be pretty rampant in the barn, and they're cool little critters. However bats come with guano.
In addition the barn is not heated, and a small tent will help to keep you warmer in the chilly spring nights. A large tent however won't be any good for warmth, and becomes cumbersome in the "tent city" that springs up in NPC camp.
On the subject of warmth, a few things of note:
LAYERS - both clothing and blankets. Unless you have an arctic rated mummy bag, you'll want an extra blanket or two in addition to your sleeping bag - remember to put layers both above and below you. You'd be amazed how much heat gets pulled from your body if the bottom isn't insulated. An air mattress, cot or camp pad is highly recommended as well, as otherwise you're sleeping on the floor. When layering clothing remember your legs too - I'm always floored by how many people will wear like 5 layers on their torso but only a single pair of pants and wonder why they're still cold. If you have underarmour, long johns or something in that vein, that's perfect.
SOCKS - cold, wet feet will suck the life out of you faster than a vampire. Whether it's from splashing in a puddle or just regular sweat, this will make you feel 10x colder. If you notice you're cold and can't seem to get warm, go change your socks. Bring at least 3 pairs per day; more if your footwear isn't really geared for hiking/outdoor activity.
BASICS - food and water. We endeavor to have snacks and water for the NPCs but it's all based on what people donate, and sometimes we just plain don't have enough, so make sure you have at least a small personal stash. If you'd like to donate to the shared snack pool you will certainly get goblin stamps for your contribution. Trail foods like granola bars and jerky are great as they will fuel you without needing refrigeration. We always have hot water going so instant foods like oatmeal or cup o noodles is also good. Water or gatorade will keep you from dehydration. And yes you can get dehydrated in the cold. In fact that's another leading cause of not being able to warm up. HQ does have a catering service for breakfast and dinner. All players (including NPCs) can order meals to be served in the tavern. Breakfast is $5 each day and dinner is $10. This must be paid on Friday night as all the food needs to be pre-ordered. Check out the HQ out-of-game section of the boards here for more details.
Doing these small things and ensuring your creature comforts make it much easier to have a good time. No matter how cool the game it's tough to get into it if you're cold, tired and hungry.