I need to install a new toilet in a camp trailer, (the flush valve has a serious leak).
Since the trailer is set-up permanently in a park I'm considering by-passing the holding tank and plumbing directly into the sewer line. Can I do this with a toilet designed for a holding tank, or should I consider a regular toilet for a house. If I use a regular toilet, does anyone make one small enough for a confined space like one in a camp-trailer.

Any help on this is appreciated, thanks.

First tell us why you want to replace the entire toilet if you just need the flush valve fixed. To a certain extent a toilet is a toilet. My fanny can't get smaller just because I'm in mobile home. Try this but they aren't very different from what I put into houses. Toilets & Replacement Parts: Mobile Home Parts Store (http://mobilehomepartsstore.com/Merchant2/merchant.mvc?Screen=CTGY&Category_Code=TL)

I need to install a new toilet in a camp trailer, (the flush valve has a serious leak).
Why throw the baby out with the bath water? Simply replace the flush valve,(see image) You will have to remove the tank,(see image) but replacing a flush valve's a easy repair.

I'm considering by-passing the holding tank and plumbing directly into the sewer line. Can I do this with a toilet designed for a holding tank
Sure you can. Just use the toilet that you have. Good luck, Tom