About tying things down;
One of the rules I follow when carrying boats is to use a minimum of 4 lines.  Two lines around the hull and one at the bow and one at the stern.  I believe 4 lines are especially important when carrying long heavy boats like canoes.  Some people use just two lines around the hull, but is that enough?  Myself, I don’t use cam locks or ratchet straps.  I tie a ‘truckers hitch’ type knot for whatever it is I’m carrying at the moment.  As far as the type of line I use, just 3/16 to 1/2 non-stretch line, old sailboat line because I happen to have lots.  I do not use old dynamic climbing line like some people do.  I find that if the line can stretch your cargo can loosen and move around.  And climbing line is too thick to tie knots.  

Gary Lee
www.vwrack.com