Pkudei - Our Journeys

For the cloud of Hashem was upon the Mishkan by day, and there was fire within it at night, before the eyes of the entire house of Israel in all their journeys
כִּי עֲנַן ה' עַל הַמִּשְׁכָּן יוֹמָם וְאֵשׁ תִּהְיֶה לַיְלָה בּוֹ לְעֵינֵי כָל בֵּית יִשְׂרָאֵל בְּכָל מַסְעֵיהֶם
Shmot 40:38
Rashi notes on the verse that where it says "מַסְעֵיהֶם" (their journeys) that "The place of their encampment is also called a journey (מַסָּע)...Since from the place of their encampment they resumed their journeys, they are all called “journeys” (מַסָעוֹת)." 

Their Journeys
However the Slonimer Rebbe in Netivot Shalom takes note of grammar of the word "מַסְעֵיהֶם". It is not simply called “journeys” (מַסָעוֹת), but rather "their journeys". Didn't Am Yisrael all travel together? Shouldn't this verse refer simply “journeys” (מַסָעוֹת)?

Ki Tisa - Preparation

You shall make a washstand of copper and its base of copper for washing, and you shall place it between the Tent of Meeting and the altar, and you shall put water therein
וְעָשִׂיתָ כִּיּוֹר נְחשֶׁת וְכַנּוֹ נְחשֶׁת לְרָחְצָה וְנָתַתָּ אֹתוֹ בֵּין אֹהֶל מוֹעֵד וּבֵין הַמִּזְבֵּחַ וְנָתַתָּ שָׁמָּה מָיִם
Shmot 30:18

The Slonimer Rebbe raises the question (Netivot Shalom), why does commandment to build the 'washstand' appear here, and not earlier with the rest of the Mishkan's vessels in Parshat Trumah?