My upgraded bed build from my previous version using pulleys and rope to this version of straps all located below the bed and self contained.

For materials used see below:

2x 1" Pillow Block Bearings - https://amzn.to/3RwE79D
1x 3/4" by 72" Black Iron Pipe - Best place to get this would be Home Depot or hardware store
9x Gear Clamps - https://amzn.to/3AKer2D
4x Ratchet Straps - https://amzn.to/3TG4cFi
1x 1/2 Flat Steel cut into 4 pieces to hold strapping down (Home Depot)
1x 1/2 Rebar - 2.5ft long depending on handle size (Home Depot)
4x Package of 4 ties downs -https://amzn.to/3QcI2aG
8x Self tapping Metal Screws - https://amzn.to/3qqsNAF
1x Electrical Tape - https://amzn.to/3qqsNAF

(All materials list are not the exact ones but the closest I could find online. Some quantities may also be larger due to buying online versus going into your local hardware store)

I hope seeing this build helped you or has given you some ideas for your current or upcoming project!