Ditto on hogflyer and aerowoof's posts. The Kadet Sr, has a big fuse, huge wing and low wing loading, as does the big Telemaster. Both have very forgiving and docile flight characteristics, and are probably the most popular video and towing platforms. If you're going to add that kind of weight and want endurance, I'd go with a G-23 Zenoah. Fairly small, it will have the needed power for the airframe and weight, it is very frugal with fuel, and since it has a magneto ignition, doesn't need an ignition battery. As long as it has fuel, it will run. 18 ounces of gas at moderate throttle settings will get you more than your 40 minutes flight time.

One thought on the Senior, with that size gas engine, you can turn as big as a 16 inch prop, more thrust per rpm, but the tricycle gear would probably not give enough ground clearance. The Telemaster is already a tail dragger, and would probably have the necessary clearance, or you could convert the Senior.

OR--- The larger, 110 size Sig Rascal would be another choice, I've seen one fly for 45 minutes with a G-26 and 18 oz of gas. It's more $$ but would make a good platform for your purposes; it flies as easily as the other two, but also has better speed and performance and will also fly very slow if needed.