We actually have quite a few people who come for several months at a time -- some on vacations but others working such as on whale sighting ships or installing solar systems at places like Costco...
Any continuous rental duration over 60 days is 45% off the base rate. Long terms are treated a bit differently in that we don't expect the whole term to be paid in advance. We ask for two months paid in advance and each new month during your stay you keep paid two months ahead until you are on your last two months (during which you would have no monies due). This seems to work well. The reason we collect for two months is that if a long term would decide to abandon the rental we have a difficult time marketing as most people book far in advance.