I have to replace the 6 panel solid wood fire door that leads from my garage into my house (the current one is slightly warped). I plan to use an Old Masters stain (to match the rest of the woodwork in my home). Is it okay to lay the door flat on a couple of saw horses and do one side at a time, or is it much better to stand it vertically and do both sides at the same time? Also, what sealer would be the best to use for an entry-type door like this one? Will the sealer go on and dry nicely if I brush it on as I don't own a sprayer? Any help would be greatly appreciated.
Yes, you can stain it on sawhorses. If you cover them with rags, then it will only be a few minutes before the stain is dry enough that you can flip the door over and do the other side. Apply the stain with an appropriate brush, and then wipe it with a lint-free rag before it tacks up. If the door is pine or another soft wood, use a wood conditioner before applying the stain.
For a door that doesn't see the elements, you can use your preference of exterior grade clear coat. Brushing is fine. Just don't put it on so heavy that it runs. That problem will mostly be alleviated by doing it on sawhorses.