It's always best to be as accurate as you can be, so....
Though I doubt the leveling of something as a trailer would matter,
since you can be off, a bit, and it not be so significant, but the
using of any tube for water leveling requires a tube whose inner
diameter is greater than 3/8". When you use a tube of 3/8" or less in
diameter, the accuracy of the level is questionable because of
adhesive forces of/within the small tube, i.e., capillary action. For
best results with your water level, use at least a 1/2" hose,
including the clear extensions you add to it. Any connecting joints,
and more so on a 3/8" or less diameter tube, further throws the
accuracy of levelness off, as well as the effect of any air bubbles
that may in the tube and/or trapped at a joint. Bubbes in the line
add to innaccuracy, also. Once you fill the hose with water, raise
the ends, high, and go along the hose, for a minute or two, and tap it
with a 'stick', as you go... this will help shake-up/make the bubbles
rise to the exits.