XC teams competing on the track if they don't have a track team

I don't believe you can do it with the coach or any of their resources. You could make a club team, though, and try to get some assistance.

You get something like a week of spring practice with the XC team. That's it. Anything else is inappropriate if the school is involved. You as the students can do whatever you want, though, and use any volunteers not on the school's payroll.

I don't know rules for things like using trainers.

It's important to note that the NCAA considers Track and Cross Country different sports, although in certain parts of the manual they impact each other closely, similar to Volleyball and Sand Volleyball being 2 different sports for NCAA purposes.

For Cross Country, DII schools without a Track Team are allowed a "non-Championship season" after XC ends in November in which they can compete in up to 5 XC meets.

If it is bona fide Track competition, organized as say a University Track Club, and that club team has open membership (i.e. not limited to just members of the school's XC team but open to the student body in general), then the NCAA considers it a separate sport and it wouldn't have an impact on XC team members NCAA eligibility. A school's XC coach can coach or advise a Track Club and the members of that Club as long as it's bona fide Track work, not merely off-season XC work in disguise. The club can be funded and receive transportation in the same way other school clubs are funded. It is important for club members to make sure they are doing Track related training and racing. If they were to call it a Track Club and not go to any meets (say do road races instead) I could see a potential violation of NCAA rules if the XC coach is working with those athletes.

For more info see the DII manual:

http://www.ncaapublications.com/productdownloads/D216.pdf