Here is a link to the Utah self decontamination certificate....
You will need documentation for each boat. Note: that you need to dry your boat for period of 7 to 30 days to qualify for 'self decontamination'. If you can't wait 7 days for the boat to dry out you are provided the 'professional decontamination' option where your boat is blasted with 1,800 psi water at 140 degrees for a min. of 10 seconds on all surfaces. This service is only offered at major reservoirs, estimated time for the decontamination procedure is 30 minute to 3 hours per boat. And you will be waiting in line with all of the motor boats that need to decontaminate as well. The decontamination is only provided during normal business hours, so you will need to plan your trip accordingly.
In theory the breakable seal that connects the boat and trailer is accepted by neighboring states. As long as the seal is not broken they can accept that the boat has not been used and is still clean. You still have to stop at all check points, but can avoid another inspection by showing them the seal and it documentation. I'm not sure how this is supposed to work for boats that are not on trailers since there is no place to attach the seal that can insure the boat has not been used.
Each state seems to have a different procedure for inspection and documentation. Utah allows you to sign the document mentioned above and claim 'self decontamination' while Colorado requires a physical inspection of each boat. Note: the Colorado inspection is void as soon as you cross in to another state, you will need a second inspection to re-enter. So if you are returning from Utah it appears that Colorado will only accept the professional decontamination with the seal.
If you travel through Nevada, Wyoming or Idaho you will also need to purchase an AIS (Aquatic Invasive Species) sticker that needs to be mounted on each boat. The average cost for an out of state boat is about $30. And you need one for each state.
I am also concerned that if you fail one of the port of entry inspections because your boat is not 'clean, drained and dry' they can impound the boat for 5 to 30 days. Considering how caked with mud my boat and trailer can get while driving the dirt road from the takeout I can only wonder how I can insure a clean boat when I encounter a random check point. Utah impounded 49 boats last year.