Mix the mustard, wine, garlic, rosemary and pepper.

Marinade the pork tenderloin in the sauce for an hour or more, up to 6 hours, in the refrigerator.

Using butchers twine, tie the pork tenderloin to the rotisserie skewer securely.  I laid one half on top of several pieces of twine, then put the skewer on top of that, then the other half of the loin on top of that.  Have the fat end of the one half of the loin match of with the skinny end of the other half so you wind up with even thickness all around.  Snug the prongs up to or into the loin to keep it from spinning on the skewer, then tie it down tight with the twine.  (see the picture above to get the idea).  Cut off any loose pieces of twine so it doesn't burn.

Prep the grill for the rotisserie, removing grates if you need to. Preheat to high, direct, as initially you will want to sear the meat to a nice golden brown.

Put the tied up tenderloin on the rotisserie and start it spinning.  Cook on high, direct heat with lid open for about 5 to 10 minutes until you have a golden brown crust.

Reduce the heat and go with a medium high, indirect heat for the remainder of the time, lid closed.

Start checking the temperature after 10 minutes, and remove from the grill when it reaches an internal temp of 140.  On my grill it took 14 minutes, but this will vary widely based on your grill and the size of the tenderloin. If your grill runs hot, or it is a small tenderloin, check it before the 10 minute mark just to be sure.  Best to use a good instant read thermometer.

After you remove from the grill, be sure to let the roast rest for about 10 minutes.  Cover in foil, then with a towel to keep it from cooling off too much.  This resting period prior to cutting keeps the juices from spilling out when you slice it and will result in a very moist slice of pork.