If you could use more space at your cottage in the summer months, consider making an very inexpensive addition to your cottage, that will not raise your taxes.
Buy a tipi or a tent.
One of the important things about the cottage, is that it be a different experience than the experience of home.
Using a tipi or a tent, constructed on a permament platform, creates an interesting and memorable experience for your guests.
People pay a lot of money to stay in ice hotels for the unusual experience of it. Your guests will have something interesting to talk about if they stay in a tipi, or a tent, when they visit you in Muskoka.
Make it a comfortable experience by having power to the structure for a coffee machine and lights, and use permament furniture like beds and night tables.
Tipis have been used at some of the older cottages for many years.
You can find excellent products on the internet at these sites www.reesetipis.com www.tipi.com www.tentsmiths.com or google tents and tipis for more information