Trailer brakes are a must, I lost my brakes once coming down a mountain due to having too much weight, almost died.
Dual axles are significantly better for many reasons. I like the truck you are using, very reliable but your gas mileage will be horrible, on par with with giant old American V8s while towing. However it is still an excellent truck you are using for reliability.
Earlier a Toyota Sequoia was mentioned, I am an avid follower of Fuelly.com a fuel mileage website. On fuelly there are 11.2 million miles logged on 623 Sequoias, they averaged 15 mpg just normal street/hwy driving (not exclusively towing), the same as Tundras on that site. I would expect MPG would be quiet a bit less towing, most people get 9-12 mpg towing with those setups that I've met.
Fuelly MPG
If you intend on permanently towing full time you can not beat an older diesel truck, specifically 2006 and older Chevy and Dodges, or 2001(?) and older 7.3 Ford diesels. The old ones all get excellent MPG.
My anecdotal evidence:
Truck camper on my wifes 2013 Gas 4.6 liter Chevy Silverado 1/2 ton truck - 10 MPG
Truck Camper on my 1993 Diesel 5.9 liter Dodge Cummins 4x4 3/4 ton truck - 15 MPG
Truck Camper on my 2003 Diesel 6.6 liter Chevy Silverado 4x4 3/4 ton truck - 15 MPG
24ft small 5th wheel on
[font=Tahoma, Verdana, Arial, sans-serif]my 2003 Diesel 6.6 liter Chevy Silverado 4x4 3/4 ton truck - 16 MPG[/font]
[font=Tahoma, Verdana, Arial, sans-serif]Same truck camper used on all 3 vehicles. I recommend Cummins engine for easiest to repair and cheapest, followed by the Ford. The Chevy Duramax diesel engines are very reliable and much faster than the other 2 brands but very expensive to repair when it breaks. The 3/4 ton and larger trucks will tow your cargo trailer like it isn't even there, 1/2 ton trucks get very sketchy in high winds and twisty mountain grades, or even when semis go flying past on long dowgrades.[/font]
[font=Tahoma, Verdana, Arial, sans-serif]The big trucks with gas engines will get about 10 mpg, but you will be totally safe towing. Unloaded their mileage is about 12 mpg[/font]
However, like I said earlier, your vehicle is a very nice reliable vehicle, just get trailer brakes and tow lightly or your truck will suffer as it is a very light duty vehicle to be towing, even as overbuilt as Toyotas are.