Actually, a fretless is super easy to intonate because all that can possibly be intonated is the 12th fret position or the octave position. If the octave harmonic of the note is exactly in tune with the fretted note at the 12th fret and the proper strings of the correct length are being used, the instrument is as good as you'll get it.
On violin family instruments (I'm including fretless bass guitars because the principle is the same), the intonation is not static. Intonation is a dynamic function! That is exactly why the URB is so much more difficult to play than a fretted bass. Intonation without frets is a function of ear training.
I'm aware that on a fretless conversion that the temptation is strong to attempt to intonate the instrument to the lines left by removing the frets. Big mistake! You can't really see the fret lines while playing without craning your neck around so you can see the board. Even when you look at your fingers you cant actually see the witness point because the pad of your finger is squished (is that a word?

) out and covers the fret lines.
If you will do these steps, in this order, you can adjust the scale length and bridge in a very few minutes.
Assuming that it's a 4 stringer and that the bass is being retuned to standard pitch after each adjustment.
1- adjust the scale length. Simply measure from the nut to the brige and adjust all the saddles to the right scale length. The proper scale length is determined by measuring from the nut to the 12th fret line. Double this measurement to derive the scale length
2- leave the G string at the proper scale length. Now shorten the D string by 1/2 the diameter of the D string.
3- repeat for the A and E strings, shortening each string by 1/2 of its own diameter.
When you reach this point the saddles will be skewed slightly.
Now Adjust the saddle on the G string untill a harmonic on the 12th fret is in tune with a fretted note on the 12th fret. Repeat on the remaining strings.
A trick that may help is to use one of the wedge shaped pencil erasers that you slide on a pencil over the regular eraser to fret the note. It will allow you to see exactly where you are fretting the notes.
Sorry for the long winded reply. Ask about anything that I've not been clear enough on. Best of luck to you.
Harrell S.