Hi Anne, welcome to the forum!
Knowing the right tax codes can always be a bit daunting so its great that you are seeking advice!
For the truck rent, we use a code called "GNR" for these types of entries. This stands for "GST Not Registered" and is basically coding it as FRE - but also giving some additional information on why this item (that normally includes GST) has been coded this way. If you don't have the GNR code you can set it up in MYOB if you feel comfortable doing that, or otherwise use the FRE code.
Your other queries:
Stamp duty - N-T
Interest Expense on a car loan - FRE
Insurance for machinery (if you mean the premium - this is GST, if you mean a payout / settlement, then N-T)
Now with the BAS payment, you should enter the amounts as N-T and against the GST clearing accounts they relate to.
e.g. GST Collected $2500.00 N-T
GST Paid -500.00 N-T
Net Payment: $2000.00
Hope this helps!