someone said the 98 and upBonnevilles cannot be siphoned with a hose down the tank is this true or should I get a locking gas cap ??

Even on my parents' 92 Olds 88, you can't siphon much out. When we swapped the pump starting with a nearly full tank, we got like a gallon out, then had to drop the end of it to get more fuel towards the neck. Could only get like 6 gallons out, and that was with the filler neck disconnected to make hose insertion easier.

Just get a locking one. Its $12. Vandals do crazy random things. Unless you live in a really rich neiborhood then your cars safe.