2015 Tundra SR5 The Only Model No Factory Bed Rails?

Recently purchased a 2015 Tundra SR5 Double Cab. I want to get a hard cover for the bed. The bed doesn't have the factory railing hardware that I can tell... just a hard plastic over bed....
- What do I need to do prior to getting a hard cover for it?
- This truck has a lift kit on it, Dealer said maybe 3 or 4 ", looks higher than that. How do I measure to confirm lift height?
- How do I identify the type of lift is on it?
- I tow a 4000lb enclosed trailer on the regular. Tundra Sags more than I like. What can I add to it so that it doesn't sag? Additional leaf spring? Air bag kit?
- Would also like to add a pull support handle on the drivers side door as the step up isn't too bad but I'd rather not use the steering wheel to hoist myself up.
Thank you in advance for whatever insight you can help with.

 

All of the 2014-2021 Tundras can accept the factory Toyota deck rail system. If there's a spray in bed liner, the holes are covered. On trucks with the factory spray in bed liner they cover the holes with paper so cleaning them out is as easy as locating them and cleaning them out with a razor. Part number for a double cab is PT278-34072

Best thing to do is figure out what type of cover you want. Some covers only use the factory deck rail, others can be installed with just clamps. Once you sort that out, you can determine if you need to add the deck rail system or not.

On the lift, the front ride height is about 22" from center of the hub to fender and rear is about 24" from center of the hub to bottom of the fender. Hard to say how much lift or what type it has just from that picture. Take some pics of front suspension.

For towing there is a range of options. The really popular one here is the Roadmaster Active Suspension. RAS is a set it and forget it system that doesn't make the ride harsher. I personally use Sumo Springs to tow a travel trailer that grosses around 4600lb loaded. Airbags are another option as well.

 

If it were a crewmax I would donate my rails for the cost of shipping

 

The bedrail is a much better cover mounting method than the clamp-on.
For years I couldn't get my Undercover Flex to stay clamped onto the left side.
Almost every time I shut it the frame came off the bed.


I ended up buying the OEM rail system and Undercover sent me the appropriate clamps for free.
Never had an issue since.

 

- It's a factory drop-in, no holes visible.

 

Also, I'm kind of bummed because I attached the enclosed trailer and took it around the block to see if it would sag, and once I detached the trailer, now the rear is now a little lower than the front and hasn't restablized back up yet.

 

As far as sag in the rear, I just added a helwig helper spring, 200 bucks and keeps the bed off the bump stops when I throw a load of dirt in there

 

Nice looking truck, drivers side grab handle will help with getting in.

 

Link if you have it, thanks

 

Looks like a big spacer and longer shock? I'm not sure I would be able to use spring helpers without removing the factory u bolts but there isn't much room on the threads. Attached are photos I took from underneath

 

Finally got around to measuring and it appears the rear is roughly 26" to 26.5" and the front is 28" - which means the rear appears to have just under 3" lift and frot has 6'?