The best I can figure is that the helms 25 weighs about 3200 lbs. With trailer and rig etc I figure maybe 4,000 all together.
It looks like a 1/2 ton truck with the right package can tow up wards of 8,000 lbs so it looks like you are will within the limits.
Just the insurance question if the contract disallows it.
8,000 lbs for a 1/2 ton truck sounds like a bit of a stretch since it fall in the realm of a class 5 tow package 7500-11,000 lbs. Still a class 3 at 3500 - 5000 lbs is within the limits as is a class 4 5000 - 7500 lbs. The class 3 would likely fit the 1/2 ton range and maybe a heavy half or 3/4 ton would have the class 4.
You can always buy an old beater pick-up for the job and only use it for towing. We own a Chevy TrailBlazer with the 129" extended wheel base and it tows our 4000 lbs of boat just fine. The inline six is rated for 5300 lbs but if you get the V8 it will tow up to 7200 lbs, the frame is rated class 4. We also find that it is an extra cost especially since we stopped towing and went for wet slip, now we tow twice a year, once in and once out. We justify the cost by the comfort of the ride and versatilty of a SUV in winter in the snow. It is pricey transportation but we still like it and won't be giving it up soon. We still have to tow the odd time and may do more in the future.