Bill,
If you have the insulators and want to use them, why
not? Even if you have the insulators and you don't want
to use them, no problem there either. The 'dislocality',
'discontinuity', impedance 'speed bump' where the ladder
line goes through the wall just isn't going to make a lot
of difference. It would just make sense to use some kind
of nonconductive material imediately around the feed line,
but going way out of your way to do so seems a bit
excessive (all things considered). I've seen ladder line
fed through an under-eave vent, routed through an attic,
laying on 'stuff', and then through a sheet rock ceiling
via a 'slit' cut with a knife. No problems with matching
or high voltage arcing even at legal limit power levels.
As for 'connections'. Make them even 'close' to right
and there should be no problems with arcing. If you're
really worried about it, stagger the connections. I've
seen some really 'fubar' installations, but never any
arcing of the ladder line, yet... Metal backed insulation
would be my biggest 'worry, but even that wouldn't cause
any loss of sleep...
'Doc