want to do it myself

First, the halfwave length of the cb frequency is 18 feet ONLY, I said only, when the signal is traveling though air. Ladies and gentlemen, the signal travels through coaxial cable between the radio and the antenna. The halfwave length of the cb frequency traveling through metal, like the the metal wire that forms the center conductor of the coaxial cable, is 11 feet 10 inches.
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Now, 18 feet of coax will work; however, since 18 feet is more than 50% longer than 11 feet 10 inches [the halfwave length of the cb frequency traveling through coaxial cable], this proves that the halfwave length of the cb frequency has absolutely no relationship to the proper length of coaxial cable. In plain english, there is no requirement for 18 feet of coax. Period.
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If you are in need of a good book on CB radio for the novice, may I suggest two books. For those that know next to nothing about cb radio, google "The Big Dummies Guide to CB Radio". While I hate the title, it is a very good book to start with and it is a very easy read. For those that know a little but not enough, google "Chilton Guide to CB Radio". The Chilton book has a terrific troubleshooting chart that alone is worth the price.

 

Only if the velocity of propagation is the speed of light. RG58 is approximately two-thirds the speed of light, so you need to reduce that 18 foot figure by 2/3 in order to be in the ballpark.

 

Actually it depends on the coax. If we're talking the better RG-58 that is foam insulated, it's right at 12 feet. if it's the crappy plastic-insulated RG-58, it's 9 feet 6 inches.

With RG8X (mini 8) it's 14 feet 9 inches.

With LMR240 it's 15 feet 2 inches.

 

I just make my own lengths or RG213 to whatever distance I'm running it in the vehicle, adjust whip length to lowest SWR, don't look back. Never had a problem.

 

This is correct. The only time coax length matters is if you're measuring SWR at the radio end of the coax.

 

which most people do.
I don't know anybody that attaches the antenna analyzer directly to the feed point of the antenna without using a piece of cable to make the connection

 

The last time I had a tunable antenna, the guy had a short jumper he used to connect the MFJ to the feedpoint. If MFJ sold a unit with a PL259 on it, that would be even better.

 

The RigExpert AA30 & AA54 have an SO239 output. Simple to connect a male-male PL259..

 

Okay, I messed up the RG58 lengths.

Plastic insulated RG58 is right at 12 feet. Foam insulated RG58 is 13 feet 1 inch.

 

Most of these guys aren't too concerned if the radio is looking at a 20 ohm load as long as the SWR is 1.5 or lower.
Null tables versus impedance Transformers isn't exactly A subject most people pay attention to.
Especially the ham guys that use a single cable for every frequency and compensate for the impedance mismatch with an antenna tuner