Ether nomenclature: Oxygens on alkyls and alkyls on alkyls Does the ether hold priority over longest chain? If so, my bet would be on:

4-(2-ethylheptanyl)oxy decane

If not, I would say:

4-(octan-2-yl methoxy) decane



Again, if ether takes precedence and not longer chain (which, if you ask me, would be ideal), I'd say:

4-[(1-methyl,2-propylheptan-1-yl)oxy]decane

If not:

4-(ethan-1-yl oxy nonan-4-yl)decane

What is correct?
Names for ethers can be formed by five different methods. Furthermore, various traditional names are retained for use in general nomenclature.

According to the current version of Nomenclature of Organic Chemistry – IUPAC Recommendations and Preferred Names 2013 (Blue Book), preferred IUPAC names of ethers $\ce{R-O-R'}$, when $\ce{R}$ and $\ce{R'}$ are both aliphatic groups, are formed by substitutive nomenclature. In substitutive nomenclature, when $\ce{R}$ is different from $\ce{R'}$, $\ce{RH}$ is chosen as parent hydride and $\ce{R'-O-{}}$ is cited as a substituent to it.


  P-63.2.2.1.1 Substituent prefix names for $\ce{R'-O-{}}$ groups are formed by concatenation, i.e., by adding the prefix ‘oxy’ to the substituent prefix name for the group $\ce{R'}$. (…)


For the first example in the question, the name of the parent hydride $\ce{RH}$ is ‘decane’.
The substituent prefix name for the group $\ce{R'-{}}$ is ‘2-ethylheptyl’.
Thus, the substituent prefix names for the $\ce{R'-O-{}}$ group is ‘(2-ethylheptyl)oxy’.
Therefore, the preferred IUPAC name of the compound is ‘4-[(2-ethylheptyl)oxy]decane’.



For the second example in the question, the name of the parent hydride $\ce{RH}$ is ‘decane’.
The substituent prefix name for the group $\ce{R'-{}}$ is ‘3-propyloctan-2-yl’.
Thus, the substituent prefix names for the $\ce{R'-O-{}}$ group is ‘(3-propyloctan-2-yl)oxy’.
Therefore, the preferred IUPAC name of the compound is ‘4-[(3-propyloctan-2-yl)oxy]decane’.