Well, you literally put the cart before the horse!
What's your reason for not buying now? Waiting for prices to come down? Can't afford or get financing? Have to have the "perfect" one for you in a time of new truck shortage?
Since you said "reliable", makes me think you're looking used. And 40' says diesel and not an old 7.3 or an old Cummins with an auto trans, or basically any pre 2008 auto Dodge, pre 2012 Powerstroke (03 to 09s should be sent to the crusher, lol), or pre 2001 Duramax.
Point is, you have ALL the other used trucks that aren't those that would be good trucks potentially and capable of what you want to do.
Whatever you spend on renting is lost, gone, bye bye. You can rent dually diesels and tow with them from places like Enterprise truck rental and equipment rental outfits. Kicker is, you'll easily spend $3k/month on rental. Unless I'm missing something, but I rent bigger pickups and class 4-5 trucks somewhat regularly. For that you could get a diesel dually, plain jane work truck. Still have to outfit it with a hitch.
The money you spend on renting, you could virtually buy a decent older diesel and have plenty of residual value when you get your preferred truck.
Or in short, renting long term for a large vehicle for personal use makes not much sense, financial or otherwise.
Or for far less than the cost of renting, you could buy a very nice older gas powered dually if you're not planning on hard miles and mountains for the next 6 months. $10-15k will get you a CHERRY old V10 Dodge or V10 Ford dually worth around 100k miles. Bonus points if you find a Dodge with a NV4500.
2016 Ram 2500, MotorOps.ca EFIlive tuned, 5” turbo back, 6" lift on 37s
2017 Heartland Torque T29 - Sold.
Couple of Arctic Fox TCs - Sold