Depends on what your definition of easy is. The fiberglass repair is certainly doable, and many Hobie 18 sailors have had to make similar repairs in the past. The trailer you're speaking of most likely has the boat supported on rollers rather than bunks or cradles, which can crack through the hull even without straps - the boat is really too heavy for so few supports, especially if the mast is allowed to rest on the aft crossbar, and considering that probably 60-70% of the boat's weight usually sits on the forward rollers alone. The proper way to support a Hobie 18 on a trailer is bunks or cradles.
The nice thing about fiberglass boats is that almost anything is repairable. The repair will take a weekend or two of your time, and will cost you ~$100 or so in materials. If you decide to try a full bottom job, it'll be several weekends and ~$300 in materials. On a scale of 1-10 Hobie repairs, this is probably around a 6. It's not terribly difficult if you're familiar with fiberglass repair, or if you take the time to fully plan the repair. It also depends on how involved you make it. The fiberglass repair itself shouldn't take more than a few days (couple weekends) to do right. If you decide to fix more, or do an entire bottom job (as many do, simply because they're halfway there), it'll get more involved. The key is to try not to do so much that you become intimidated by it or overwhelmed.
Here's someone that decided to go above and beyond to repair the bottom of the boat and then some:
viewtopic.php?f=13&t=12641Hobie Hotline article on major fiberglass repairs (page 14):
http://www.w1dm.com/projects/hotline/08 ... OTLINE.pdfHobie Hotline article on small hole repairs (page 16):
http://www.w1dm.com/projects/hotline/08 ... OTLINE.pdfHobie Hotline article on bottom jobs (page 12):
http://www.w1dm.com/projects/hotline/08 ... OTLINE.pdfA basic overview of fiberglass/gel coat repairs:
https://www.youtube.com/watch?v=rz5WCfipaNwMore in-depth instructional video on fiberglass repairs (watch the whole series - 4 parts):
https://www.youtube.com/watch?v=i9hfpOCnzEsFiberglass and gel coat work really is a lot more simple and a lot easier than a lot of people might think. It just takes a bit of forethought. If you're really not sure about making the repair yourself, you can always have it repaired professionally by any boat repair shop, but you can expect that to cost somewhere between $400 and $1500, depending on how much you want repaired.